Usually a PartManager only listens for events (for activation/selection) for one toplevel widget (and its children), the one specified in the constructor. Sometimes however (like for example when using the KDE dockwidget library), it is necessary to extend this.

Specifies whether the partmanager should handle/allow nested parts or not.

This is a property the shell has to set/specify. Per default we assume that the shell cannot handle nested parts. However in case of a KOffice shell for example we allow nested parts. A Part is nested (a child part) if its parent object inherits KParts::Part. If a child part is activated and nested parts are not allowed/handled, then the top parent part in the tree is activated.